YOUNG HERON: Young herons impacted by oil from the Deepwater Horizon oil spill are seen at the Fort Jackson Wildlife Rehabilitation Centre.

OIL SPILL: The Taiwanese skimmer dubbed "A Whale", left, conducts a test of its oil skimming capabilities in the Gulf of Mexico as part of the Deepwater Horizon oil spill response.

BP STICKS AT IT: Work continues at the site of the BP oil well leak in the Gulf of Mexico.

GULF SPILL: Gas and oil continue to leak at the Deepwater Horizon oil spill site in the Gulf of Mexico, in this image captured from a BP live video feed.

GULF SPILL: Oil-tainted water from the Gulf of Mexico sits in jars placed before a group of business people and officials called Gulf Voices as they speak of their plight during a visit to Capitol Hill in Washington.

UNDER THE SEA: AP journalist Rich Matthews takes a closer look at oil from the Deepwater Horizon spill, in the Gulf of Mexico.

UNDERWATER OIL: Patches of oil from the Deepwater Horizon spill are seen from an underwater vantage.

OIL SPILL: Patches of oil from the Deepwater Horizon spill are seen from an underwater vantage.

UNDERWATER VANTAGE: patches of oil from the Deepwater Horizon spill are seen from underwater.

EFFECTS: Marine reef ecologist Scott Porter holds barnacle samples he removed from an oil rig in waters in the Gulf of Mexico. Porter plans to determine the effect of oil from the Deepwater Horizon spill.

Marine reef ecologist Scott Porter works to remove oil from the Deepwater Horizon spill off his hands.

CONTAMINATION: CNN reporter Anderson Cooper lays down on the bow of an air boat to take a picture as Governor Bobby Jindal, right, removes a fishing net from the oil contaminated water in Pass A Loutre near Venice, Louisiana.

GULF OIL SPILL: Oil fouls the water near nesting pelicans on an island in Barataria Bay just off the the coast of Louisiana.

PELICAN COVERED IN OIL: An oiled bird on an island in Barataria Bay just off the the coast of Louisiana.

US lawmakers and local residents clamored on Sunday for BP and the Obama administration to do more to save the Gulf Coast from an out-of-control oil spill that has become the biggest environmental catastrophe in the country's history.

Lawmakers from US President Barack Obama's own Democratic Party called the nearly six-week oil gush in the Gulf of Mexico an "environmental crime" and demanded $1 billion from BP to protect the region's treasured marshlands.

The failure on Saturday of a "top kill" technique attempted by London-based BP to try to seal its leaking Gulf well has unleashed a surge of anger that poses a major domestic challenge to Obama and his party in an election year.

"This is probably the biggest environmental disaster we have ever faced in this country," White House adviser Carol Browner told NBC's "Meet the Press."

The Gulf spill has surpassed the Exxon Valdez disaster off Alaska in 1989 as the worst US oil spill, with an estimated 12,000 to 19,000 barrels (1.9 million to 3 million liters) leaking per day.

Given the enormity of the disaster, critics say Obama was too slow to respond.

"I hold Obama responsible for not making BP stand up and look at the people in the face and fix it," said Dean Blanchard, owner of a seafood business, who spoke at a protest rally in New Orleans on Sunday.

"It's not right what is going on, I didn't do nothing wrong, I didn't deserve this," he told the hundreds of protesters, some of whom carried signs, such as "Seize BP."

BP Chief Executive Tony Hayward, the target of ire over his company's failures to stop the spill and protect vital wetlands, apologized to Gulf Coast residents.

"The first thing is to say we're sorry, we're sorry for the massive disruption it's caused their lives, there's no one who wants this thing over more than I do," Hayward said as he visited the fishing hub of Venice on Sunday.

Hayward had predicted that despite risks, the top kill had a 60 to 70 percent chance of success. He said he did not know why it failed to stop the gusher.

The next BP step would involve undersea robots using diamond-rimmed saws to cut off a pipe over the well to put in place a containment device that would try to siphon off most of the leaking oil and gas up to a tanker ship on the surface.

It has never been attempted at the depth of the BP well, 1.6km under water.

Even Hayward conceded on Sunday that "there's no doubt that the ultimate solution is the relief well, which is in August."

The possibility of another two months to a definitive solution could spell more financial trouble for BP, whose market value has dropped by 25 percent since the Deepwater Horizon rig exploded, killing 11 workers, and triggering the spill.

Obama, who has called the spill a "man-made disaster," has relied on BP and its deep-sea technology to try to stop the leak, although he has made clear the government is in charge.

Critics argue, however, that he has not directed enough resources to the unfolding disaster and he has not been present enough.

The White House said on Sunday that the government will triple clean-up resources in areas affected by the spill, while the administration's top energy and environment officials head back to the Gulf this week following Obama's second visit on Friday.

BP and the entire US oil industry face more probing questions about why safety backups did not accompany their pursuit of oil in ever deeper offshore waters.

"I think without question if the word criminal should be used in terms of an environmental crime against our country, that what's going on in the Gulf of Mexico is going to qualify," US Democratic Representative Ed Markey told CBS' "Face the Nation."

Department of Justice officials are part of an ongoing federal investigation into the rig explosion and the Obama administration has not ruled out the possibility of a criminal prosecution.

In Louisiana, which has borne the brunt of the oil spill impact so far, authorities demanded that BP and the federal government rush a plan to create a sand barrier to the oil by dredging and building up outlying sandbanks and islets.

"I'm devastated ... We are dying a slow death, every time that oil takes out a piece of the marsh, a piece of Louisiana is gone forever," said Billy Nungesser, president of Plaquemines Parish, told CNN.

Louisiana Democratic Senator Mary Landrieu called on BP to immediately invest $1 ($NZ1.47) billion to protect marshes, wetlands and estuaries across the region. "While we may not be able to plug the leaking well right away, there is nothing that should stop us from getting help to the Gulf Coast immediately," she said.

Gulf residents fear the oil slick could be whipped further inshore by what forecasters predict will be the most active Atlantic storm season since 2005, the year of Hurricane Katrina.

That deadly storm proved a political disaster for President George W. Bush, who was accused of complacency in handling it, and Obama is fighting to prevent the Gulf spill from becoming his own "Katrina" ahead of the November congressional elections.

At the New Orleans protest, Jennifer Jones said Louisianians still recovering from Katrina's devastation are frustrated by the response thus far.

"We need the help again, continuing from Katrina, this is like Part Two," Jones said.